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Subject[patch 6/7] sched: use rq->avg_event to resurrect nohz ratelimiting
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Entering nohz at high frequency eats cycles, ratelimit it
just as we do idle_balance(), and for the same reason.

Signed-off-by: Mike Galbraith <efault@gmx.de>

---
include/linux/sched.h | 2 ++
kernel/sched/core.c | 7 +++++++
kernel/time/tick-sched.c | 2 +-
3 files changed, 10 insertions(+), 1 deletion(-)
Index: linux-3.0-tip/include/linux/sched.h
===================================================================
--- linux-3.0-tip.orig/include/linux/sched.h
+++ linux-3.0-tip/include/linux/sched.h
@@ -1988,8 +1988,10 @@ static inline void idle_task_exit(void)

#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
extern void wake_up_idle_cpu(int cpu);
+extern int sched_needs_cpu(int cpu);
#else
static inline void wake_up_idle_cpu(int cpu) { }
+static inline void sched_needs_cpu(int cpu) { }
#endif

extern unsigned int sysctl_sched_latency;
Index: linux-3.0-tip/kernel/sched/core.c
===================================================================
--- linux-3.0-tip.orig/kernel/sched/core.c
+++ linux-3.0-tip/kernel/sched/core.c
@@ -587,6 +587,13 @@ static inline bool got_nohz_idle_kick(vo
return idle_cpu(smp_processor_id()) && this_rq()->nohz_balance_kick;
}

+#ifdef CONFIG_SMP
+int sched_needs_cpu(int cpu)
+{
+ return cpu_rq(cpu)->avg_event < sysctl_sched_migration_cost;
+}
+#endif
+
#else /* CONFIG_NO_HZ */

static inline bool got_nohz_idle_kick(void)
Index: linux-3.0-tip/kernel/time/tick-sched.c
===================================================================
--- linux-3.0-tip.orig/kernel/time/tick-sched.c
+++ linux-3.0-tip/kernel/time/tick-sched.c
@@ -352,7 +352,7 @@ void tick_nohz_stop_sched_tick(int inidl
} while (read_seqretry(&xtime_lock, seq));

if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
- arch_needs_cpu(cpu)) {
+ arch_needs_cpu(cpu) || sched_needs_cpu(cpu)) {
next_jiffies = last_jiffies + 1;
delta_jiffies = 1;
} else {



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